1. Technical Field
The present invention relates to a polarization element and a projector.
2. Related Art
Recent years, wire grid polarization elements have been known as optical elements having a polarization separation function. The wire grid polarization elements are each obtained by forming nanoscale thin metal wires on a transparent substrate such as a glass substrate so as to line the substrate with the metal wires. The wire grid polarization elements have a characteristic of having a high polarization separation performance, and in addition, being superior in heat resistance to polarization elements made of organic materials since the wire grid polarization elements are made of inorganic materials. Therefore, use of wire grid polarization elements instead of polarization separation elements in the related art made of polymeric materials is considered in various optical systems. Specifically, the wire grid polarization elements are preferably used as polarization elements for light valves of liquid crystal projectors exposed to the light from high power light sources, and are disposed in front of and behind (at lest either one of the light entrance side and the light exit side) the light valves.
Incidentally, in the light exit side of the light valves, the function of absorbing the unwanted polarized light is required. This is because, if the unwanted polarized light is reflected by the light exit side of the light valve, there might arise a problem that the reflected light enters the light valve again to cause temperature rise in transistors, which makes the grayscales out of order, or to become stray light, which degrades the image quality.
Therefore, there has been considered various types of wire grid polarization elements of an absorption type provided with a function of absorbing the unwanted polarized light. For example, in JP-A-2005-37900 (Document 1), the unwanted polarized light is selectively absorbed by a polarization element having a first grating layer with light reflecting property formed on a substrate attached with a second grating layer (an absorbing layer) with a light absorbing property.
On the other hand, in JP-A-2006-133275 (Document 2), there is proposed a polarization element having a light transmissive substrate having steps formed on the surface with a pitch longer than the wavelength of the incident light, and light reflecting bodies arranged on the surface of the light transmissive substrate in a striped manner with a pitch shorter than the wavelength of the incident light. Thus, the stray light is prevented from occurring by reflecting the unwanted polarized light component with an angle but not specularly.
However, in Document 1, since deposition of the absorbing layer is required in addition to formation of the polarization element, and therefore, the structure of the element becomes complicated, the manufacturing cost rises. Further, in Documents 1 and 2, there is no description regarding the technology of absorbing the unwanted polarized light using surface plasmon resonance (SPR).